At the present, for filling up the excavations effected on the ground for laying pipings, sewages and the like, after these pipings, sewages, etc. have been laid they are covered with compacting material so as to keep them in position and to close the excavations, and as material therefor concrete of conventional kind is normally used, which is poured in position, or some embankment earth or loose tombstone material (sand, crushed stone, coarse gravel) is utilized, or a combination of materials, concrete and embankment earth or tombstone material which are suitably mixed with each other are utilized.
The use of the above-mentioned filling and compacting materials, however, gives raise to some drawbacks. In fact, first of all these materials are not able to perform effective sealing of the pipings, sewages and the like which have been laid underground, due to the difficulty of these materials to distribute themselves for filling all the areas around the pipings and sewages, and under these circumstances inadequate sealing may sometime occur at the junctions of such pipings and sewages, with consequent outgoing and loss of the fluid transported through such pipings and sewages. This phenomenon tends to occur when using both fluid concretes and embankment earth or loose tombstone material, and with these later materials which are denser and less fluid the above phenomenon is particularly emphasized, owing to the greater difficulty of these materials to uniformly distribute themselves on all the positions of pipings and sewages.
Another drawback of the use of the current materials is due to the difficulty of arranging the excavation filling and sealing material which is submitted to continuous loads produced by vehicular traffic passing over the same material and tends to yield slowly and progressively, particularly in the case in which the material is embankment earth or tombstone material, and this material has been covered with a road surface. Also in this case, the use of compacted tombstone material involves a more accentuated phenomenon, since a slow and progressive crushing in position of the weaker tombstone elements and a penetration of the stiffer tombstone elements on the more yieldable original ground may occur.
Finally, the use of these filling and sealing materials involves the drawback that the same materials are difficult to remove, when such removal is needed for maintenance or repair works of pipings, sewages etc. and it is very difficult and burdensome if the used material is concrete.